The invention relates generally to thermal transfer devices, and particularly, to solid-state thermal transfer devices.
Thermal transfer devices may be used for a variety of heating/cooling and power generation/heat recovery systems, such as refrigeration, air conditioning, electronics cooling, industrial temperature control, waste heat recovery, and power generation. These thermal transfer devices are also scalable to meet the thermal management needs of a particular system and environment. Unfortunately, existing thermal transfer devices, such as those relying on refrigeration cycles, are relatively inefficient and environmentally unfriendly due to mechanical components such as compressors and the use of refrigerants.
In contrast, solid-state thermal transfer devices offer certain advantages, such as the potential for higher efficiencies, reduced size and weight, reduced noise, and being more environmentally friendly. For example, thermotunneling devices transfer heat by tunneling hot electrons from one electrode to another electrode across a nanometer-scale barrier. The heat transfer efficiency of these thermotunneling devices depends upon various factors, such as material characteristics (e.g., electrodes and barrier), electrode alignment, electrode spacing, and thermal losses. For example, the efficiency of these thermotunneling devices generally improves if the electrodes have a low work function, the barrier is in vacuum or an inert gas, and the spacing between the electrodes is less than about 50 nanometers. Unfortunately, electrode spacing is particularly difficult to achieve and maintain in these thermotunneling devices. Thus, achieving efficient thermotunneling devices can be problematic.
Certain other solid-state thermal devices, such as thermoelectric devices, transfer heat by flow of electrons through pairs of p-type and n-type semiconductor thermoelements forming thermocouples that are connected electrically in series and thermally in parallel. The heat transfer efficiency of these thermoelectric devices depends on the Seebeck coefficient, the electrical conductivity, and the thermal conductivity of the thermoelectric materials employed for such devices. For example, the efficiency of these devices generally improves if the thermal conductivity of the thermoelectric material is low (less than about 10E-3 W/cmK). Unfortunately, these devices have a relatively low efficiency (of the order of 2-3%,) due to the relatively high thermal conductivity (greater than about 20E-3) of the thermoelectric materials such as skutterudite based thermoelectric materials. Thus, achieving efficient thermoelectric devices can be problematic.
Accordingly, a need exists for creating a thermal transfer device with low work function electrodes and a controlled spacing between the electrodes. Furthermore, it would be desirable to create a thermal transfer device with low thermal conductivity.